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.Dd September 18, 2023
.Dt SAVE-ENTROPY 8
.Os
.Sh NAME
.Nm save-entropy
.Nd Save bits of entropy to feed /dev/random at startup
.Sh SYNOPSIS
.Nm save-entropy
.Sh DESCRIPTION
The
.Nm
command is used to save entropy data from
.Pa /dev/random
to files in a specified output location.
The files saved are used at startup to provide additional entropy for
.Pa /dev/random .
The output file will be different in every invocation until the maximum number
of different files is reached.
(See
.Em entropy_save_num
for details).
By default this script is invoked via
.Xr cron 8
every eleven minutes approximately.
.Pp
This command does nothing if executed inside a
.Xr jail 8 .
.Pp
Three variables in
.Pa /etc/rc.conf
regulate the behavior of the script:
.Bl -tag -width Ds
.It Va entropy_dir
Specify the directory for saved entropy files.
Defaults to
.Pa /var/db/entropy .
If set to "NO" it disables caching entropy via
.Xr cron 8 .
This setting is shared with
.Pa /etc/rc.d/random .
.It Va entropy_save_sz
Size of the entropy cache files.
Defaults to 4096.
.It Va entropy_save_num
Number of entropy cache files to save.
Defaults to 8.
.El
.Sh FILES
.Bl -tag -width Ds
.It Pa /etc/rc.conf
.El
.Sh EXIT STATUS
.Ex -std
Errors will be recorded in the system log.
.Sh SEE ALSO
.Xr syslog 3 ,
.Xr random 4 ,
.Xr rc.conf 5 ,
.Xr cron 8
.Sh HISTORY
The
.Nm
command first appeared in
.Fx 5.0 .
.Sh AUTHORS
The
.Nm
command was originally written by
.An Doug Barton <dougb@FreeBSD.org> .
This manual page was written by
.An Fernando Apesteguia <fernape@FreeBSD.org> .
